The construction of a moving-slit chest radiographic unit for reduction of scattered radiation will be completed. The performance characteristics of the instrument will be tested in studies on phantoms. The device will also be used on patients suspected of having lung nodules, and results compared to those obtained by convention chest radiography. Factors affecting perception of chest nodules will be sutided, especially the influence of nodule location and contrast. Other methods of improving radiographic contrast, such as improved grid designs will also be studied.